Blood Urea Nitrogen (BUN) Reaction Slide was studied and primarily applied in clinical laboratory as a method for BUN test it is ideal of emergency use. BUN Reaction slide is a dry chemical reagent pad, also it is a separation couple-seal system. The slide is divided into two chambers by a membrane, the up one is UN enzymatic reaction area, the bottom one is detector reaction part. This system eliminated interference from blood pH, Hb and bilirubin, only 5 minutes is needed for a single test. The test within day and day-to-day CVs were < 5.5%. Test linearity was up to 1000 mg/L. There was good correlation with BUN enzyme-couple method, r = 0.985, y = 0.91 X + 3.9. The acurrate was better than BUN Strip method.